[erlang-questions] Architecture question: logging inside library

Dmitry Kolesnikov <>
Mon Jan 11 09:39:50 CET 2016


Hello,

I am using macro to wrap logger library. 
This gives me a freedom to config desired library and behavior at build time.  


-ifndef(EMERGENCY).
-define(EMERGENCY(Fmt, Args), lager:emergency(Fmt, Args)).
-endif.

-ifndef(ALERT).
-define(ALERT(Fmt, Args), lager:alert(Fmt, Args)).
-endif.

-ifndef(CRITICAL).
-define(CRITICAL(Fmt, Args), lager:critical(Fmt, Args)).
-endif.

-ifndef(ERROR).
-define(ERROR(Fmt, Args), lager:error(Fmt, Args)).
-endif.

-ifndef(WARNING).
-define(WARNING(Fmt, Args), lager:warning(Fmt, Args)).
-endif.

-ifndef(NOTICE).
-define(NOTICE(Fmt, Args), lager:notice(Fmt, Args)).
-endif.

-ifndef(INFO).
-define(INFO(Fmt, Args), lager:info(Fmt, Args)).
-endif.

-ifdef(CONFIG_DEBUG).
   -define(DEBUG(Str, Args), lager:debug(Str, Args)).
-else.
   -define(DEBUG(Str, Args), ok).
-endif.


Best Regards,
Dmitry


> On Jan 11, 2016, at 9:34 AM, Max Lapshin <> wrote:
> 
> Hi.
> 
> As we know, it is good when library doesn't have any hardcoded dependencies at all.
> 
> I don't understand what is a good way to remove lager (or any other logging library) from library dependencies.
> 
> 
> For example, we have an mpegts decoder/encoder library. This library takes binary and unpacks it to list of frames or packs back:
> 
> mpegts_decoder:decode(Binary,  mpegts_decoder:init(Options)) ->  {ok, Frames, State}
> 
> 
> There are calls to lager in some places of code that are used for indicating some statuses:
> 
> dump_psi(Decoder, NewPMT),
> lager:info("PMT: ~p", [Descriptors]),
> ...
> 
> 
> What is the proper way to refuse from adding logger as a dependency for such pure library?
> Pass a callback into  initialisation options?
> 
> 
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> 
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